Spoon 1/3 cup of the tomato mixture into 6-quart slow cooker. Top with single layer of noodles, breaking them to fit as necessary. Add half the Swiss chard. Dollop with one-third of ricotta mixture and one-third of remaining tomato mixture. Sprinkle with one-third of mozzarella.

Repeat layers twice, ending with mozzarella. Cover and cook on Low for 2 to 3 hours, or until noodles are tender.